Generally, in order to detect electrocardiogram (ECG) or heartbeats, an electrode should be directly bright into contact with the skin, which is inconvenient in various ways. For this reason, various kinds of non-contact electrodes have been developed.
As an existing technique, Korean Patent Registration No. 10-0948941 discloses an apparatus and method for measuring an impedance change of a wrist portion caused by a heartbeat by using an electrode having inductance, which includes a measuring unit for generating an oscillation signal, generating a composite oscillation signal by sensing a change of an external electric and magnetic field, differentiating the measured electric and magnetic field signal to generate a differential signal, and generating a detection signal according to a breath and heartbeat wavelength condition of body, and a signal processing unit for receiving the detection signal output from the measuring unit and extracting a heartbeat signal. This technique has a distinctive feature in the measuring unit and the signal processing unit when an inductive electrode is applied to measure a heartbeat, and a magnetic field is generated as the electrode receives the oscillation signal. In addition, when the electrode generates a composite oscillation signal combined with a bio signal, the state of the electrode is important, for example an adhesion state of the electrode to a human body. In Korean Patent Registration No. 10-0948941, it is impossible to precisely detect a change of a bio signal.
For this, the inventors of this application also have a patent with Korean Patent Registration No. 10-1302000, disclosing an electrode for an inductance-type bio-signal sensor in which a conductive thread-based or conductive textile-based coil-type magnetic field sensor forms a circular spiral coil or a rectangular spiral coil between two textiles and an anti-contact unit made of an insulation material is provided between the coil threads (for example, an insulating thread is stitched).
FIG. 1 is a diagram for illustrating a configuration for detecting a volume change by using a change of inductance by using the conductive textile-based inductance-type bio-signal measurement sensor disclosed in Korean Patent Registration No. 10-1302600.
An inductance-type bio-signal measurement sensor 10 is mounted, and a signal detector 30 is mounted to an outer side of the inductance-type bio-signal measurement sensor. The detector includes an oscillating unit 50 and a demodulating unit 70.
The oscillating unit 50 is composed of an oscillation circuit having L and C to transmit a vibration signal to the inductance-type bio-signal measurement sensor 10.
The inductance-type bio-signal measurement sensor 10 is configured to maximize sensitivity by disposing a ferromagnetic substance core capable of focusing a magnetic flux on a center portion of the coil. In other words, a volume of interest (VOI) 20 may cause a temporal variation, formed by a geometric structure of a coil sensor, namely influenced by a magnetic force, and the conductive textile-based inductance-type bio-signal measurement sensor 10 senses a change of eddy current caused by electric conductivity of a substance located in the volume.
If the inductance-type bio-signal measurement sensor 10 receives a vibration signal, a magnetic field of a time-varying function is formed in a living body in the volume of interest (VOI) 20, and the generated magnetic field creates an eddy current in the substance. The inductance of the sensor is influenced by a movement of a detection target. Therefore, a vibration signal of the heart muscle causes a change of inductance of the coil, and this signal is transmitted through the oscillating unit 50 to the demodulating unit 70.
In detail, a magnetic field is formed by a current minutely flowing on the coil of the inductance-type bio-signal measurement sensor 10. The magnetic field varying according to time induces an eddy current in a detection target (or, in a human body), and the formed induced current generates a minute magnetic field in a direction opposite to the magnetic field formed at the coil. The change of the magnetic field of the coil of the inductance-type bio-signal measurement sensor 10 results in a variation of the inductance (the induced magnetic field) of the coil. To detect the variation, the oscillating unit 50 serving as an oscillation circuit is provided to regard the coil of the inductance-type bio-signal measurement sensor 10 as an inductor circuit, and in this case, a frequency modulation representing a variation of a frequency of an oscillator is exhibited due to a movement of a detection target (in a human body). As one of detection methods, the demodulating unit 70 may trace a modulated frequency by using a phase-locked loop (PLL). If this frequency demodulation is used, a movement of the detection target is exhibited as a PLL output, which allows a movement of the heart to be measured.
Generally, in the bio-signal detection, a bio signal is rarely detected with a single electrode, and two or more electrodes including a reference electrode and a signal electrode are used to detect a bio signal. Therefore, a dual electrode or an array electrode is desired. If a plurality of electrodes is provided like this case, a signal to be detected may be induced to another electrode and thus detected erroneously. Therefore, the electrode structure is very important.
In addition, for allowing a bio signal to be measured during activity, a flexible electrode is demanded.
Moreover, a conductive textile-based inductance-type electrode apparatus for bio-signal detection which has a switch for turning on or off an array electrode is also demanded.